build: fix Lua build

build: fix Lua build

Each of Lua's major versions are incompatible with each other. Ubuntu,
at least, does not provide a single liblua.so or /usr/include/lua; all
SOs and headers are versioned, e.g. liblua5.3.so and
/usr/include/lua5.3. There's already an m4 macro in the GNU collection
to handle this situation, so let's use that.

This allows building with Lua enabled to work on platforms other than
Fedora.

* Move lib/lua.[ch] -> lib/frrlua.[ch] to prevent path conflicts
* Fix configure.ac search for proper CPP and linker flags
* Add Lua include path to AM_CPPFLAGS
* Update vtysh/extract.pl.in

Signed-off-by: Quentin Young <qlyoung@cumulusnetworks.com>